The present invention relates to a gauge, i.e. a testing device.
More particularly, the invention relates to a gauge for inspecting and indicating the quality of gear teeth on a workpiece.
Gears are known in many varieties and for multitudinous applications; for example, in mechanical machines gears are used for furnishing or transmitting motive power. Gears may have internal and/or external teeth and be constructed as spur gears, helical gears or involute gears. It is also known to use diverse kinds of gauges to check the quality of the gear teeth on such gears, i.e. whether the teeth are properly oriented, whether they are within the permissible tolerances, and the like.
One prior-art gauge, intended particularly for the testing of internal teeth on a gear, has two contact pins which are arranged symmetrically with reference to a longitudinal axis of the gauge and are movable radially. The free ends of these pins each are ball-shaped or carry a ball-shaped portion.
These pins are inserted into the confines of the internal gear to be checked; during this insertion the pins are in a radially retracted position. However, they are being biased in radially outward direction by a spring so that, when they are in place for performing the check, their ball-shaped ends are pressed by this spring in the radially outward direction until they enter between the flanks of the teeth to be inspected. A lengthwise movable rod is connected to the pins and moves through a distance which depends upon the extent of the radially outward movement of the pins. This lengthwise movement of the rod is a measure of the tooth quality and is transmitted to an external indicator, such as a dial.
A problem with this prior-art device is that the pins must be very precisely inserted into the teeth being checked, so that their contact faces (i.e. the ball-shaped portions) are located exactly in a plane that is common to them as they contact the teeth of the gear. This is an extremely difficult undertaking, unless one uses an alignment rod or similar fixture in order to position the two pins in a common plane and keep them there. Consequently, the use of such a fixture is necessary; however, the use of the fixture, especially of an alignment rod, in turn requires the presence of a planar abutment surface against which the fixture can rest at the end opening where the gauge is being inserted. Quite often, such an abutment face does not exist or is not planar or not sufficiently planar. This requires either that the workpiece must be deliberately provided with such an abutment face (meaning an additional operating step and consequent increase in manufacturing costs), or else the absence of the abutment face makes taking an accurate measurement that much more difficult.